⏱ 8 min read Distributed Counter System: Low-Level Design A distributed counter tracks a numeric value that many servers increment or decrement concurrently — […] Read article

⏱ 10 min read Cost Allocation System: Low-Level Design A cost allocation system attributes infrastructure spend to the teams, products, or customers that generated Read article

⏱ 9 min read A/B Experiment System: Low-Level Design An A/B experiment system assigns users to treatment groups, measures whether a metric changes between Read article

⏱ 9 min read Feature Rollout System: Low-Level Design A feature rollout system lets engineering teams deploy code to production while controlling which users Read article

⏱ 10 min read GDPR Article 17 grants users the “right to erasure” — the ability to request that all their personal data be Read article

⏱ 9 min read A cursor-based incremental sync system lets clients efficiently download only the data that has changed since their last sync, rather Read article

⏱ 8 min read A webhook delivery system pushes event notifications to customer-configured HTTP endpoints — the foundation of Stripe, GitHub, Shopify, and Twilio’s Read article

⏱ 9 min read A referral tracking system attributes new user signups to the existing user who referred them, enabling reward programs and measuring Read article

⏱ 9 min read A poll system lets users create questions with multiple choice answers, vote on them, and see real-time results. Used in Read article

⏱ 8 min read A bookmark (save) system lets users collect and organize content they want to revisit — articles, products, listings, posts. Core Read article

⏱ 10 min read A content tagging system lets users and systems attach descriptive labels to content — blog posts, products, images, videos — Read article

⏱ 9 min read A content reporting and abuse detection system allows users to flag harmful content — spam, harassment, hate speech, illegal material Read article

⏱ 8 min read An idempotency key service ensures that retried API requests do not cause duplicate side effects — a critical requirement for Read article

⏱ 10 min read Multi-factor authentication (MFA) adds a second verification layer beyond passwords — protecting accounts even when passwords are compromised. The three Read article

⏱ 9 min read A data archival system moves aged, infrequently accessed data from hot storage (fast, expensive) to warm or cold tiers (slower, Read article